The Six Books of Proclus on the Theology of Plato, Volume 2

For, if it be possible, let there be two things which thus subsist; since there will be the same impossibility if there are more than two; or let that which subsists primarily consist of both these. But if indeed it consists of both, it will again be one, and there will not be two things that are first. And if it be one of the two, each will not be first. Nor if both are equally primary, will each have a principal subsistence. For if one of them is primary, but this is not the same with the other, what will it be in that order? For that subsists primarily, which is nothing else than that which it is said to be. But each of these being different is, and at the same time is not that which it is said to be.

If, therefore, these differ from each other, but they do not primarily differ so far as they are that which they are said to be; for this primarily suffers that which is the same; both will not be first, but that of which both participating, are said to subsist primarily.

From these things it is evident, that what is primarily being is one alone, and that there are not two primary beings, or more than two; that the first intellect is one alone, and that there are not two first intellects; and that the first soul is one. This is also the case with every form, such as the primarily beautiful, and the primarily equal. And in a similar manner in all things. Thus also, with respect to the form of animal, and the form of man, the first of each is one; for the demonstration is the same.